The isPrototypeOf() method checks if an object exists in another object's prototype chain.

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isPrototypeOf() differs from the instanceof operator. In the expression "object instanceof AFunction", the object prototype chain is checked against AFunction.prototype, not against AFunction itself.

Syntax

prototypeObj.isPrototypeOf(object)

Parameters

object

The object whose prototype chain will be searched.

Return value

A Boolean indicating whether the calling object lies in the prototype chain of the specified object.

isPrototypeOf() method, along with the instanceof operator particularly comes in handy if you have code that can only function when dealing with objects descended from a specific prototype chain, e.g., to guarantee that certain methods or properties will be present on that object.